The evaluation of the effectiveness of medical care relies largely on the assessment of health status. The development of validated instruments to conceptualise and quantify health has developed rapidly but barriers remain to the wider dissemination and acceptance of health status as medical outcome measures. These include the need for additional normative data to describe change in health status over time in a healthy population, so that the meaning of unit change in health status can be better understood. Influences on health status other than medical care are currently not well defined and their effect needs to be quantified. The Whitehall II study can contribute vital information to such research. A cohort of 10,308 white-collar workers was established in 1985 to investigate the causes of socioeconomic differences in health. The role of psychosocial factors such as work characteristics and social support in explaining social differences in health since 1985 has included: two physical examinations; collection of sickness absence data (including medical confirmation of long spells) and notification of deaths and cancer registrations. The SF-36 General Health Survey was included in the latest examination of participants. This instrument has been validated in this general working population by comparison with other health measures from the examination. Short-term reliability of the SF-36 has also been examined. Data on the distribution of health status across social groups and the social determinants of health status have been collected and preliminary analysis performed. The aims of the next phase of the study are: 1) to document changes in health status in the participants over time; and 2) to continue the analysis and investigation of the social determinants of change in health status. A second assessment of health status, as measured by the SF-36, is planned for late 1994 using a postal questionnaire, an average of two and a half years after the initial assessment. In addition to the continued follow-up using established mechanisms in the interim period, details of major medical events, serious illnesses or hospitalization will also be collected in this questionnaire. The analysis of this data will both describe and explain change in health status. the effect of social factors on health status, controlling for medical events, will be a particular focus of the analysis.